Electrodeposition of bright nickel

ABSTRACT

Acid nickel plating bath for obtaining bright nickel deposits, said bath being of the chloride, sulfate, fluoborate or sulfamate type and containing a brightener mixture comprising the disodium salt of methylene bis naphthalene sulfonic acid and a second component selected from coumarin, piperonal bisulfite complex, sodium beta-styrene sulfonate, benzimidazole and mixtures thereof, with the proviso that benzimidazole is used only when greater than 50 mole percent of nickel salt used in the bath is nickel fluoborate.

I United States Patent [151 3,66 1 ,73 1 Schevey 1 May 9, 1972 541 ELECTRODEPOSITION OF BRIGHT 3,305,462 2/1967 Ostrow et al .204/49 NICKEL 3,306,831 2/1967 Cope, Jr. ....204 43 3,312,604 4/1967 Wells et al. ....204/49 Inventor: Wflham Schevey, Hewley, 3,429,789 2/1969 Ostrow et a] .204 49 [73] Assignee: Allied Chemical Corporation, New York, a

Primary Exammer-G. L. Kaplan Attorney-Emest A. Polin [22] Filed: Mar. 16, 1970 21 Appl. No.: 20,031 [57] ABSTRACT Acid nickel plating bath for obtaining bright nickel deposits, [52] U S Cl 204/49 said bath being of the chloride, sulfate, fluoborate or sulfa- [51] 5/08 mate type and containing a brightener mixture comprising the l 58] Fieid M9 43 44 disodium salt of methylene bis naphthalene sulfonic acid and a second component selected from coumarin, piperonal bisulfite complex, sodium beta-styrene sulfonate, [56] References Cited benzimidazole and mixtures thereof, with the proviso that n- STATES PATENTS benzimidazole is used only when greater than 50 mole percent of nickel salt used in the bath is nickel fluoborate. 3,219,559 11/1965 Ostrow et a1 ..204/49 3,305,461 2/1967 Ostrow et a1 ..204/49 13 Claims, No Drawings BACKGROUND OF THE INVENTION Acid nickel plating baths normally yield dull electrodeposits, but bright deposits can be obtained by the addition of effective amounts of certain organic compounds, known as brighteners.

It is the object of this invention to provide a novel mixture of brighteners for use in acid nickel plating baths.

It is a further object to provide improved acid nickel bath compositions for bright nickel plating.

It is still another object to provide an improved method for obtaining bright nickel electrodeposits.

SUMMARY or THE INVENTION It has been discovered that when both Brightener A and Brightener B, defined below, are added in sufficient amounts to a conventional acid nickel plating bath of the sulfate, chloride, fluoborate or sulfamate type, a bright nickel electrodeposit is obtained which is superior to the deposit obtained when only one of Brightener A or Brightener B is added to the bath.

The plating bath comprises an aqueous acid solution of nickel salt selected from the group consisting of nickel sulfate, nickel chloride, nickel fluoborate, nickel sulfamate or mixtures thereof.

Brightener A is the disodium salt of methylene bis naphthalene sulfonic acid and has the structural formula:

it 114/ (I) SOSNH 3. sodium beta-styrene sulfonate, having the structural formula:

4. benzimidazole, having the structural formula:

5. mixtures thereof, with the proviso that benzimidazole is used only when greater than 50 mole percent of nickel salt used in the bath is nickel fluoborate. Preferably benzimidazole is used only when greater than about 80 mole percent of nickel salt is nickel fluoborate.

DETAILED DESCRIPTION Brightener A and Brightener B are each added to the plating bath in amounts sufficient to obtain a bright nickel electrodeposit. Generally, the concentrations of Brightener A and of Brightener B dissolved in the nickel plating bath independently range from about 0.1 to about 10 grams per liter of plating bath, but not exceeding the saturation concentration thereof. Although some of the brightener compounds have saturation concentrations greater than 10 grams per liter, no advantage is seen from the use of such higher concentration. Preferably the concentrations of Brightener A and Brightener B independently range from about 0.12 to about 2.0 grams per liter but not exceeding the saturation concentration thereof.

While Brightener A and Brightener B can each be added to the nickel plating bath separately, it is preferred that they first be premixed, so that they can be added to the bath in one step. This mixture, called the brightener mixture, should contain sufficient amounts of Brightener A and Brightener B so that when the mixture is added to the plating bath, the above indica'ted bath concentrations will be satisfied.

A convenient method of adding the brightener mixture to the plating bath is to first prepare a solution of the brightener mixture, and then add said solution to the plating bath. The solvent used in preparing the solution of brightener mixture should be soluble in the plating bath. Preferably the solvent is selected from the group consisting of water, aliphatic monohydric alcohols having from one to three carbon atoms and mixtures thereof. The aliphatic monohydric alcohols are methanol, ethanol, n-propanol and isopropanol, with isopropanol being preferred. When the brightener mixture includes coumarin, it is preferred that the solvent contain at least 25 volume percent alcohol.

The ratio of Brightener A to Brightener B in the brightener mixture or dissolved in the bath is not critical, but generally the weight ratio varies from about 0.l:l to about 10:], preferably from about 05:1 to about 2:1.

The brightener mixtures of this invention are generally compatible with addition agents conventionally employed in plating baths, for example, wetting agents, such as sodium lauryl sulfate and castile soap, antifoam agents, stress relief agents and the like.

It is a preferred embodiment of this invention that the brightener mixtures be used in conjunction with saccharin. Saccharin has the effect of reducing the stress and brittleness of the nickel deposit and also somewhat increases the brightness of the deposit. Generally, the concentration of saccharin ranges from about 0.1 gram per liter of plating bath to its saturation concentration, preferably from about 0.5 to about 2.0 grams per liter of plating bath.

Saccharin may be added to the bath separately or it may first be incorporated as part of the brightener mixture. In the latter case, the amount of saccharin in the brightener mixture is not critical as long as the amount is sufficient to supply the above indicated concentrations of saccharin in the bath. Generally, the weight ratio of saccharin to brightener mixture varies from about 0.l:l to about lOzl, preferably from about 1:1 to about 8:1.

The bright nickel deposit is obtained in conventional manner by passing a current through a nickel plating bath containing Brightener A and Brightener B, between the anode, which is typically nickel, and the cathode, which is the article to be plated.

Temperature, current density, pH, and other operating conditions are relevant only as far as they influence the basic characteristics of the plating bath in known manner. Thus operating conditions commonly employed with the conventional nickel plating solutions may be employed when those solutions contain the brightener mixtures.

Generally, plating bath temperatures may vary from about 40 to about 170 F preferably from about to about F.

Current density generally ranges from about 1 to about 300 amps per square foot, preferably from about to about 150 amps per square foot. For plating of wires, current densities as high as 600 amps per square foot can be employed. With Watts Nickel type baths, however, lower current densities are generally employed, usually up to about 80 amps per square foot, with up to about 100 amps per square foot for wires.

Values for bath pH generally range from about 2.5 to about 5.0, preferably from about 3.5 to about 4.5. A bath pH between about 5.0 and about 7.0 can also be employed, but at these pH values, the bath usually requires the addition of nickel complexing agents, e.g. citric acid, malic acid or ammonium hydroxide.

It is preferred that during the plating process relative movement be provided between the plating bath and the object being plated. Any conventional means for agitating the bath or for moving the object being plated may be employed. Illustrative of such means are mechanical stirring of the bath, passage of compressed air through the bath, cathode rod agitation, and the like.

The baths listed in the following table illustrate, but do not limit, the types of electroplating baths in which the brightener mixtures of this invention may be incorporated as addition agents in the above indicated proportions. The composition ranges generally employed in the art are stated for each of the baths in grams per liter of bath.

The above nickel baths generally may contain minor amounts of other nickel salts. For example, the above fluoborate bath may additionally contain nickel chloride or nickel sulfate, usually in such amounts that at least about 80 mole percent of the nickel salt is nickel fluoborate.

The preferred bath is a nickel fluoborate bath wherein the nickel fluoborate concentration ranges from about 220 to 440 grams per liter, especially wherein at least about 80 mole percent of the nickel salt is nickel fluoborate.

The invention can be more fully understood by reference to the following examples. I

EXAMPLE 1 Tests were carried out in a heated 267 ml Hull Cell, plating onto brass Hull Cell panels. All samples were compared at one to two amps. The plating solution was a nickel fluoborate solution having the following characteristics:

l qh 440 grams/liter H 4 Temperature 1 10 F.

Runs were made both with and without air agitation of the solutions. I

The various brighteners used and descriptions of the resultant platesare listed in Table II below. In Table ll the units g/l" refer to grams of brightener per liter of plating bath. The term Tamol N is a trademark for a mixture of disodium salts of methylene bis naphthalene sulfonic acid. The term Heloplex is a trademark for piperonal bisulfite comstyrene sulfonate Plus agitation .l5 g./l. Tamol N .15 g./l. sodium betastyrene sulfonate 11A) .15 g./l.TamolN .15 g./l. sodium betastyrene sulfonate Plus agitation .l5 g./l. Tamol N .l5 g./l. sodium betastyrene sulfonate l.0 g./l. saccharin 12A) .15 g./l. Tamol N .l5 g./l. sodium beta styrene sulfonate 1.0 g./l. saccharin Plus agitation .l5 g./l. Heloplex l3A) .l5 g./l. Heloplex Plus agitation .l5 g./l. Tamol N .l5 g./l. Heloplex 14A) .15 g./l. Tamol N .l5 g./l. Hcloplex Plus agitation .l5 g./l. Tamol N .15 g./l. l-leloplex 1.0 g./l. saccarin 15A) .15 g./l. Tamol N l6A) .l5 g./l. coumarin .l5 g./l. sodium betastyrene sulfonate plex.

TABLE II Brightener Plate Description y 1) Blank Dull 1A) Blank plus agitation Dull 2) .l5 g./l. Tamol N Bright below 20 amps/sq. ft. 2A) .l5 g./l. Tamol N Bright below 20 amps/sq. ft.

Plus agitation 3) .l5 g./l. Tamol N Semi-bright 1.0 g./l. saccharin 3A) .15 g./l. Tamol N Semi-bright 1.0 g./l. saccharin Plus agitation 4) .l5 g./l. coumarin Dull 4A) .15 g./l. coumarin Dull with bright spots Plus agitation Y 5) .15 g./l. coumarin Bright with gas bubble .l5 g./l. Tamol N streaks 5A) .15 g./l. coumarin Bright .l5 g./l. Tamol N Plus agitation 6) .l5 g./l. coumarin Bright, but pitted .l5 g./l. Tamol N l.0 g./l. saccharin 6A) .l5 g./l. coumarin Bright .l5 g./l. Tamol N 1.0 g./l. saccharin Plus agitation 7) .l5 g./l. benzimidazole Dull with bright spots 7A) .15 g./l. benzimidazole Dull with bright spots Plus agitation 8) .l5 g./l. Tamol N Bright .l5 g./l. benzimidazole 8A) .15 g./l. Tamol N Bright .l5 g,/l. benzimidazole Plus agitation 9) .l5 g./l. Tamol N Bright, put pitted .l5 g./l. benzimidazole 1.0 g./l. saccharin 9A) .15 g./l. Tamol N Bright 715 g./l. benzimidazole 1.0 g./l. saccharin Plus agitation l0) .l5 g./l. sodium beta- Semi-bright styrene sulfonate 10A) .15 g./l. sodium beta- Semi-bright Semi-bright (but brighter than run 10) Bright Bright Bright Dull, bright streak at 12 amps/sq. ft. Dull with bright streak Bright, but pitted Bright Bright Bright Dull Dull with bright spots Plus agitation .15 g./l. Heloplex .15 g./l. coumarin .15 g./l. l-leloplex .15 g./l. coumarin 1.0 g./l. saccharin .lS g./l. Heloplex .15 g./l. benzimidazole .15 g./l. Heloplex .15 g./l. benzimidazole 1.0 g./l. saccharin 20A) .l g./l. Heloplex .15 g./l. benzimidazole 1.0 g./l. saccharin Plus agitation l7) Dull with bright spots l8) Dull with bright spots 19) Bright streaks 20) Dull with bright spots Dull with bright spots EXAMPLE 2 The tests of Example 1 are repeated using a Watts Nickel type bath having the following characteristics:

NiSO 6H O 300 grams/liter NiCl 6H O 45 grams/liter Boric Acid 30 grams/liter pH 4 Temperature 1 F.

Results substantially similar to those of example 1 are obtained, except that no brightening is observed when brightener mixtures containing benzimidazole are used.

EXAMPLE 3 The tests of example 1 are repeated using a nickel sulfamate bath having the following characteristics:

Boric Acid 30 grams/liter pH 4 Temperature 1 10 F.

nickel sulfamate and mixtures thereof, the improvement which comprises incorporating therein, in amounts sufiicient to obtain a bright nickel deposit, the disodium salt of methylene bis naphthalene sulfonic acid (Brightener A) and a component selected from the group consisting of coumarin, piperonal bisulfite complex, sodium beta-styrene sulfonate, benzimidazole and mixtures thereof (Brightener B), with the proviso that benzimidazole is used only when greater than 50 mole percent of nickel salt used in the bath is nickel fluoborate.

2. The bath of claim 1 wherein the concentrations of Brightener A and Brightener B independently range from about 0.1 to 10 grams per liter of bath, but not exceeding their saturation concentrations.

3. The bath of claim 2 wherein greater than 50 mole percent of nickel salt used in the bath is nickel fluoborate and Brightener B is benzimidazole;

4. The bath of claim 3 wherein greater than mole percent of the nickel salt is nickel fluoborate.

5. The bath of claim 2 wherein Brightener B is coumarin.

6. The bath of claim 2 wherein Brightener B is piperonal bisulfite complex.

7. The bath of claim 2 wherein Brightener B is sodium betastyrene sulfonate.

8. The bath of claim 2 which additionally contains saccharin in a concentration ranging from about 0.1 gram per liter to its saturation concentration.

9. The bath of claim 1 wherein the concentrations of Brightener A and Brightener B independently range from about 0.12 to 2.0 grams per liter of bath, but not exceeding their saturation concentrations.

10. The bath of claim 9 wherein at least about 80 mole percent of the nickel salt is nickel fluoborate and the nickel fluoborate concentration ranges from about 220 to about 440 grams per liter of bath.

11. The bath of claim 9 which additionally contains saccharin in a concentration ranging from about 0.5 to about 2.0 grams per liter of bath.

12. A nickel plating process comprising passing a current from an anode to a cathode through the bath of claim 1.

13. A nickel plating process comprising passing a current from an anode to a cathode through the bath of claim 8. 

2. The bath of claim 1 wherein the concentrations of Brightener A and Brightener B independently range from about 0.1 to 10 grams per liter of bath, but not exceeding their saturation concentrations.
 3. The bath of claim 2 wherein greater than 50 mole percent of nickel salt used in the bath is nickel fluoborate and Brightener B is benzimidazole.
 4. The bath of claim 3 wherein greater than 80 mole percent of the nickel salt is nickel fluoborate.
 5. The bath of claim 2 wherein Brightener B is coumarin.
 6. The bath of claim 2 wherein Brightener B is piperonal bisulfite complex.
 7. The bath of claim 2 wherein Brightener B is sodium beta-styrene sulfonate.
 8. The bath of claim 2 which additionally contains saccharin in a concentration ranging from about 0.1 gram per liter to its saturation concentration.
 9. The bath of claim 1 wherein the concentrations of Brightener A and Brightener B independently range from about 0.12 to 2.0 grams per liter of bath, but not exceeding their saturation concentrations.
 10. The bath of claim 9 wherein at least about 80 mole percent of the nickel salt is nickel fluoborate and the nickel fluoborate concentration ranges from about 220 to about 440 grams per liter of bath.
 11. The bath of claim 9 which additionally contains saccharin in a concentration ranging from about 0.5 to about 2.0 grams per liter of bath.
 12. A nickel plating process comprising passing a current from an anode to a cathode through the bath of claim
 1. 13. A nickel plating process comprising passing a current from an anode to a cathode through the bath of claim
 8. 